Steam turbine having a brush seal assembly

ABSTRACT

A steam turbine having a shaft and a first (e.g., high-pressure) turbine section. A first embodiment also includes a first bearing longitudinally spaced apart from the first turbine section and further includes a first brush-seal assembly, having bristles, longitudinally positioned between the first turbine section and the first bearing and radially positioned proximate the shaft. The steam turbine is devoid of any backup seal to the bristles. In a second embodiment, a second brush seal assembly is positioned between the first and second (e.g., intermediate-pressure) turbine sections which lack any intervening bearing.

FIELD OF THE INVENTION

The present invention relates generally to steam turbines, and moreparticularly to a steam turbine having a steam-path seal assembly.

BACKGROUND OF THE INVENTION

A steam turbine has a steam path which typically includes, inserial-flow relationship, a steam inlet, a turbine, and a steam outlet.A gas turbine has a gas path which typically includes, in serial-flowrelationship, an air intake (or inlet), a compressor, a combustor, aturbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage,either out of the gas or steam path or into the gas or steam path, froman area of higher pressure to an area of lower pressure, is generallyundesirable. For example, gas-path leakage in the turbine or compressorarea of a gas turbine, between the rotating rotor shaft of the turbineor compressor and the circumferentially surrounding turbine orcompressor casing, will lower the efficiency of the gas turbine leadingto increased fuel costs. Also, steam-path leakage in the turbine area ofa steam turbine, between the rotating shaft of the turbine and thecircumferentially surrounding casing, will lower the efficiency of thesteam turbine leading to increased fuel costs.

The turbine portion of a steam turbine typically includes ahigh-pressure turbine section, perhaps an intermediate-pressure turbinesection, and a low-pressure turbine section each having rotatablesteam-turbine blades fixedly attached to, and radially extending from, asteam-turbine shaft which is rotatably supported by bearings. Thebearings usually are located longitudinally outward from the high andlow-pressure turbine sections and longitudinally between the high andintermediate-pressure turbine sections. Usually the steam pressure dropthrough a high-pressure or an intermediate-pressure turbine section isat least generally 2,000 kPa (kiloPascals), and the difference inpressure of the steam entering the high and intermediate-pressureturbine sections is at least generally 600 kPa. It is noted that thesteam exiting the high-pressure turbine section normally is reheated bythe boiler before entering the intermediate-pressure turbine section andthat the "steam" exiting the low-pressure turbine section enters acondenser before being directed to the boiler, as is known to theartisan.

Labyrinth seals have been used to minimize steam-path leakage betweenthe high-pressure turbine section and its longitudinally-outwardbearing, between the low-pressure turbine section and itslongitudinally-outward bearing, and between the high andintermediate-pressure turbine sections. Such labyrinth seals consist oflongitudinally spaced-apart rows of labyrinth seal teeth. Many rows ofteeth are needed to seal against the high-pressure differentials foundin a typical steam turbine, and this has contributed to the impressivelongitudinal length (sometimes over fifteen meters) of a standard steamturbine used by power utilities to turn a generator for the productionof electricity. Such length has required extra bearings to support thesteam-turbine rotor.

It is noted that brush seals are used to minimize leakage through a gapbetween two components, wherein such leakage is from a higher pressurearea to a lower pressure area. Brush seals have been used, or their useproposed, in rotating machinery. Such use or proposed use includes, butis not limited to, turbomachinery including steam turbines and gasturbines used for power generation and gas turbines used for aircraftand marine propulsion. It is noted that brush seals minimize the leakageof steam in steam turbines and minimize the leakage of compressed air orcombustion gases in gas turbines.

The brush seals usually have wire or ceramic bristles conventionallywelded or otherwise affixed to a backing plate. To improve performance,such brush seals typically align their wire bristles to contact therotating rotor shaft at an angle between generally forty-five andgenerally sixty degrees with respect to a radius line from the center ofthe rotor to the point of bristle contact. For high pressureapplications, a seal plate is positioned against the seal bristles onthe downstream side (i.e., lower-pressure side) of the brush seal. Brushseals do a better sealing job than labyrinth seals, as can beappreciated by the artisan. However, all known steam turbines or steamturbine designs which rely on a brush seal assembly between turbinesections or between a turbine section and a bearing also rely on astandard labyrinth seal which acts as a backup seal for the brush sealassembly.

SUMMARY OF THE INVENTION

In a first preferred embodiment, the steam turbine of the inventionincludes a steam-turbine shaft, a first turbine section, a firstbearing, and a first brush-seal assembly. The first turbine section hasrotatable steam-turbine blades fixedly attached to, and radiallyextending from, the shaft. The first bearing is longitudinally spacedapart from the first turbine section and rotatably supports the shaft.The first brush-seal assembly is longitudinally positioned between thefirst turbine section and the first bearing and is radially positionedproximate the shaft. The first brush seal assembly includes bristles,and the steam turbine is devoid of any backup seal to the bristles ofthe first brush seal assembly.

In a second preferred embodiment, the steam turbine of the inventionincludes a steam-turbine shaft, a first turbine section, a secondturbine section, and a second brush-seal assembly. The first and secondturbine sections each have rotatable steam-turbine blades fixedlyattached to, and radially extending from, the shaft. The second turbinesection is longitudinally spaced apart from the first turbine sectionwithout an intervening bearing. Steam enters the second turbine sectionat a different pressure than the steam which enters the first turbinesection. The second brush-seal assembly is longitudinally positionedbetween the first and second turbine sections and is radially positionedproximate the shaft. The second brush seal assembly includes bristles,and the steam turbine is devoid of any backup seal to the bristles ofthe second brush seal assembly.

In a third preferred embodiment, the steam turbine of the inventioncombines the features of the first and second preferred embodiments.Preferably, the first brush-seal assembly is the only seallongitudinally positioned between the first turbine section and thefirst bearing and radially positioned proximate the shaft, and thebristles of the first brush-seal assembly provide generallyone-hundred-percent of the steam-sealing capability of the first brushseal assembly. Likewise, it is preferred that the second brush-sealassembly is the only seal longitudinally positioned between the firstand second turbine sections and radially positioned proximate the shaft,and the bristles of the second brush-seal assembly provide generallyone-hundred-percent of the steam-sealing capability of the second brushseal assembly.

Several benefits and advantages are derived from the invention. Thebristles of the brush seal assemblies provide better steam-sealingcapability than do the teeth of a labyrinth seal assembly. Also, andmost importantly, the use of brush seal bristles alone, without anylabyrinth backup seal, will dramatically shorten the longitudinal lengthof the steam turbine. With Applicants' invention, the length of atypical steam turbine can be reduced from generally fifteen meters togenerally nine meters, and a bearing supporting the steam-turbine shaftcan be removed that would otherwise be located between the high andintermediate pressure turbine sections.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, partially cross-sectional view of a preferredenablement of the steam turbine of the present invention;

FIG. 2 is an enlarged view of a portion of the steam turbine of FIG. 1showing the first brush seal assembly and surrounding area;

FIG. 3 is an enlarged view of a portion of the steam turbine of FIG. 1showing the first turbine section (i.e., the high-pressure turbinesection) and surrounding area;

FIG. 4 is an enlarged view of a portion of the steam turbine of FIG. 1showing the second brush seal assembly and surrounding area; and

FIG. 5 is an enlarged view of a portion of the steam turbine of FIG. 1showing the second turbine section (i.e., the intermediate-pressureturbine section) and surrounding area.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, FIGS. 1-3 schematically show a preferredenablement of the steam turbine 10 of the present invention. In a firstpreferred embodiment of the invention, the steam turbine 10 includes asteam-turbine shaft 12 having a generally longitudinally-extending axis14. The shaft 12 may comprise a single monolithic shaft or may comprisetwo or more shaft sections which are affixed together to create theoverall shaft 12. It is understood, for the purpose of describing thepresent invention, that the term "shaft" includes "disc" or "wheel" andthe like.

The steam turbine 10 also includes a first turbine section 16 havingrotatable steam-turbine blades 18 fixedly attached to, and radiallyextending from, the shaft 12. The blades 18 are also known as buckets orairfoils. The terminology "fixedly attached to" means the blades 18 turnwith the shaft 12. It is understood that the blades 18 may be detachedfrom the shaft 12 for inspection, repair, replacement, and the like.Typically, the blades 18 extend radially outward from the shaft 12.Steam enters the first turbine section 16 at a first pressure.Preferably, the first turbine section 16 is a high-pressure turbinesection wherein the steam pressure drop through the first turbinesection 16 is at least generally 2,000 kPa (kiloPascals). In a typicalsteam turbine design, the first pressure is between generally 8,300 kPaand generally 24,000 kPa, and the pressure of the steam exiting thefirst turbine section 16 is generally 4,000 kPa.

The steam turbine 10 additionally includes a first bearing 20longitudinally spaced apart from the first turbine section 16 androtatably supporting the shaft 12. Preferably, the first bearing 20 is acombination journal and thrust bearing as can be appreciated by thoseskilled in the art. A tapered land or tilting pad bearing is typicallyused.

The steam turbine 10 moreover includes a first brush-seal assembly 22longitudinally disposed between the first turbine section 16 and thefirst bearing 20 and radially disposed proximate the shaft 12. The firstbrush seal assembly 22 includes a plurality of bristles 24 (most clearlyshown in FIG. 2) having tips which preferably generally contact theshaft 12. The steam turbine 10 is devoid of any backup seal (such as,but not limited to, a labyrinth seal) to the bristles 24 of the firstbrush seal assembly 22. For the purpose of describing the presentinvention, a steam turbine is said to be devoid of any backup seal tothe bristles of a brush seal assembly longitudinally disposed between aturbine section and a bearing if the steam-leakage rate between theturbine section and the bearing would at least double if all of thebristles of the brush seal assembly were removed. It is understood thatthe bristles 24 of the first brush seal assembly 22 may comprise one ormore packets of bristles and that such packets may be located only inone area or may be longitudinally spaced apart from each other so as tobe positioned at discrete sealing locations. It is further understoodthat the first brush-seal assembly 22 may contain, in addition to thebristles 24, other types of seals including, without limitation,labyrinth seals but only if the other types of seals are being used asprimary (and not backup) seals. However, it is preferred that thebristles 24 of the first brush seal assembly 22 provide at leastgenerally ninety-percent of the total steam-sealing capability of allseals taken together which are longitudinally disposed between the firstturbine section 16 and the first bearing 20 and radially disposedproximate the shaft 12. In an exemplary enablement, the first brush sealassembly 22 is the only seal longitudinally disposed between the firstturbine section 16 and the first bearing 20 and radially disposedproximate the shaft 12. In a preferred embodiment, the bristles 24 ofthe first brush-seal assembly 22 provide generally one-hundred-percentof the steam-sealing capability of the first brush seal assembly 22.

Other components of the steam turbine 10 include a (typicallystationary) casing 26 which is radially spaced apart from and generallycircumferentially surrounds the shaft 12 and the first turbine section16. The first bearing 20 and the first brush seal assembly 22 areattached to the casing 26. A first conduit 28 directs steam from aboiler 30 to the inlet of the first turbine section 16, and a secondconduit 32 directs steam from the outlet of the first turbine section 16back to the boiler 30 for reheating.

In a second preferred embodiment of the invention, the steam turbine 10includes the shaft 12 and the first turbine section 16 of the firstpreferred embodiment. Additionally, the steam turbine 10 includes asecond turbine section 34 longitudinally spaced apart from the firstturbine section 16 without an intervening bearing. The second turbinesection 34 has rotatable steam-turbine blades 36 fixedly attached to,and radially extending from, the shaft 12. Steam enters the secondturbine section 34 at a second pressure which is different from thefirst pressure. Preferably, the second turbine section 34 is anintermediate-pressure turbine section wherein the steam pressure dropthrough the second turbine section 34 is at least generally 2,000 kPaand wherein the difference between the first pressure of the firstturbine section 16 and the second pressure of the second turbine section34 is at least generally 600 kPa. In a typical steam turbine design, thesecond pressure is generally 4,000 kPa, and the pressure of the steamexiting the second turbine section 34 is generally 1,000 kPa.

Further, the steam turbine 10 includes a second brush-seal assembly 38longitudinally disposed between the first and second turbine sections 16and 34 and radially disposed proximate the shaft 12. The second brushseal assembly 38 includes a plurality of bristles 40 having tips whichpreferably generally contact the shaft 12. The steam turbine 10 isdevoid of any backup seal (such as, but not limited to, a labyrinthseal) to the bristles 40 of the second brush seal assembly 38. For thepurpose of describing the present invention, a steam turbine is said tobe devoid of any backup seal to the bristles of a brush seal assemblylongitudinally disposed between two turbine sections if thesteam-leakage rate between the two turbine section would at least doubleif all of the bristles of the brush seal assembly were removed. It isunderstood that the bristles 40 of the second brush seal assembly 38 maycomprise one or more packets of bristles and that such packets may belocated only in one area or may be longitudinally spaced apart from eachother so as to be positioned at discrete sealing locations. It isfurther understood that the second brush-seal assembly 38 may contain,in addition to the bristles 40, other types of seals including, withoutlimitation, labyrinth seals but only if the other types of seals arebeing used as primary (and not backup) seals. However, it is preferredthat the bristles 40 of the second brush seal assembly 38 provide atleast generally ninety-percent of the total steam-sealing capability ofall seals taken together which are longitudinally disposed between thefirst and second turbine sections 16 and 34 and radially disposedproximate the shaft 12. In an exemplary enablement, the second brushseal assembly 38 is the only seal longitudinally disposed between thefirst and second turbine sections 16 and 34 and radially disposedproximate the shaft 12. In a preferred embodiment, the bristles 40 ofthe second brush-seal assembly 38 provide generally one-hundred-percentof the steam-sealing capability of the second brush seal assembly 38.

Other components typically found in the steam turbine 10 include alow-pressure turbine section 42, a second bearing 44, and a condenser46. Steam typically enters the low-pressure turbine section 42 atgenerally 150 psia and exits the low pressure turbine section 42 atsubatmospheric pressure. A third conduit 48 directs steam from theboiler 30 to the inlet of the second turbine section 34, a fourthconduit 50 directs "steam" from the outlet of the second turbine section34 to the condenser 46, and a fifth conduit 52 returns the condensedsteam from the condenser 46 back to the boiler 30. It is noted that thecasing 26 (which may be a single monolithic casing or attached-togetherlongitudinal casing segments) additionally is radially spaced apart fromand generally circumferentially surrounds the second turbine section 34and the low-pressure turbine section 42. The second bearing 44 and thesecond brush seal assembly 38 are attached to the casing 26. Preferably,the second bearing 44 is a tilting pad bearing.

In a third preferred embodiment of the invention, the steam turbine 10combines the components previously described for the first and secondpreferred embodiments. It is pointed out that FIG. 2 shows an enlargedfirst brush seal assembly 22 and surrounding area of the steam turbine10. The bristles 24 each have a fixed end which is attached to a plate54 which is itself attached to the casing 26. The bristles 24 each havea free end (i.e., a tip) which is disposed proximate (and preferablygenerally contacts) the shaft 12. It is also pointed out that FIG. 3shows an enlarged first turbine section 16 and surrounding area of thesteam turbine 10. It is seen that vanes 56 are attached to, and radiallyextend inwardly from, the casing 26. Likewise, FIG. 4 shows an enlargedsecond brush seal assembly 38 and surrounding area of the steam turbine10. The bristles 40 each have a fixed end which is attached to a plate58 which is itself attached to the casing 26. The bristles 40 each havea free end (i.e., a tip) which is disposed proximate (and preferablygenerally contacts) the shaft 12. Also, FIG. 5 shows an enlarged secondturbine section 34 and surrounding area of the steam turbine 10. It isseen that vanes 60 are attached to, and radially extend inwardly from,the casing 26. Preferred materials for the bristles 24 and 40 include,without limitation, coated or uncoated metal (including alloy) wirebristles and ceramic wire bristles. Preferably, the steam turbine of thepresent invention is a large utility steam turbine or a combined cyclesteam turbine which is used to power one or more generators producing atotal of at least two-hundred megawatts of electricity.

The foregoing description of several preferred embodiments of theinvention has been presented for purposes of illustration. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be defined by the claims appended hereto.

What is claimed is:
 1. A steam turbine comprising:a) a steam-turbineshaft having a generally longitudinally-extending axis; b) a firstturbine section having rotatable steam-turbine blades fixedly attachedto, and radially extending from, said shaft, wherein steam enters saidfirst turbine section at a first pressure; c) a second turbine sectionlongitudinally spaced apart from said first turbine section without anintervening bearing and having rotatable steam-turbine blades fixedlyattached to, and radially extending from, said shaft, wherein steamenters said second turbine section at a second pressure which isdifferent from said first pressure; and d) a second brush-seal assemblylongitudinally disposed between said first and second turbine sectionsand radially disposed proximate said shaft, wherein said second brushseal assembly includes a plurality of bristles, and wherein said steamturbine is devoid of any backup seal to said bristles of said secondbrush seal assembly.
 2. The steam turbine of claim 1, wherein saidbristles of said second brush-seal assembly provide at least generallyninety-percent of the total steam-sealing capability of all seals takentogether which are longitudinally disposed between said first and secondturbine sections and radially disposed proximate said shaft.
 3. Thesteam turbine of claim 2, wherein the steam pressure drop through eachof said first and second turbine sections is at least generally 2,000kPa, and wherein the difference between said first pressure of saidfirst turbine section and said second pressure of said second turbinesection is at least generally 600 kPa.
 4. The steam turbine of claim 3,wherein said second brush-seal assembly is the only seal longitudinallydisposed between said first and second turbine sections and radiallydisposed proximate said shaft.
 5. The steam turbine of claim 4, whereinsaid bristles of said second brush-seal assembly provide generallyone-hundred-percent of the steam-sealing capability of said second brushseal assembly.
 6. A steam turbine comprising:a) a steam-turbine shafthaving a generally longitudinally-extending axis; b) a first turbinesection having rotatable steam-turbine blades fixedly attached to, andradially extending from, said shaft, wherein steam enters said firstturbine section at a first pressure; c) a first bearing longitudinallyspaced apart from said first turbine section and rotatably supportingsaid shaft; d) a first brush-seal assembly longitudinally disposedbetween said first turbine section and said first bearing and radiallydisposed proximate said shaft, wherein said first brush seal assemblyincludes a plurality of bristles, and wherein said steam turbine isdevoid of any backup seal to said bristles of said first brush sealassembly; e) a second turbine section longitudinally spaced apart fromsaid first turbine section without an intervening bearing and havingrotatable steam-turbine blades fixedly attached to, and radiallyextending from, said shaft, wherein steam enters said second turbinesection at a second pressure which is different from said firstpressure; and f) a second brush-seal assembly longitudinally disposedbetween said first and second turbine sections and radially disposedproximate said shaft, wherein said second brush seal assembly includes aplurality of bristles, and wherein said steam turbine is devoid of anybackup seal to said bristles of said second brush seal assembly.
 7. Thesteam turbine of claim 6, wherein said bristles of said first brush-sealassembly provide at least generally ninety-percent of the totalsteam-sealing capability of all seals taken together which arelongitudinally disposed between said first turbine section and saidfirst bearing and radially disposed proximate said shaft.
 8. The steamturbine of claim 7, wherein the steam pressure drop through said firstturbine section is at least generally 2,000 kPa.
 9. The steam turbine ofclaim 8, wherein said first brush-seal assembly is the only seallongitudinally disposed between said first turbine section and saidfirst bearing and radially disposed proximate said shaft.
 10. The steamturbine of claim 9, wherein said bristles of said first brush-sealassembly provide generally one-hundred-percent of the steam-sealingcapability of said first brush seal assembly.
 11. The steam turbine ofclaim 10, wherein said bristles of said second brush-seal assemblyprovide at least generally ninety-percent of the total steam-sealingcapability of all seals taken together which are longitudinally disposedbetween said first and second turbine sections and radially disposedproximate said shaft.
 12. The steam turbine of claim 11, wherein thesteam pressure drop through second turbine section is at least generally2,000 kPa.
 13. The steam turbine of claim 12, wherein the differencebetween said first pressure of said first turbine section and saidsecond pressure of said second turbine sections is at least generally600 kPa.
 14. The steam turbine of claim 13, wherein said secondbrush-seal assembly is the only seal longitudinally disposed betweensaid first and second turbine sections and radially disposed proximatesaid shaft.
 15. The steam turbine of claim 14, wherein said bristles ofsaid second brush-seal assembly provide generally one-hundred-percent ofthe steam-sealing capability of said second brush seal assembly.